1. Field of the Invention
This invention relates to stents of improved configuration which incorporate spiral articulations which unwind to form bracing structures or scaffolding upon expansion.
2. Brief Description of the Prior Art
Stents are radially expandable endoprosthesis which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. They have also been implanted in urinary tracts and bile ducts. They are used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon.
In the past, stents have assumed many configurations and been made of many materials, including metals and plastic. Ordinary metals such as stainless steel have been used as have shape memory metals such as nitinol and the like. Stents have also been made of biodegradable plastic materials. They have been formed from wire, tube stock, etc.
This invention provides a new configuration for stents which may be adapted by all of the various types of prior art stents referred to hereinabove. There are numerous advantages to the new configuration. It limits recoil and adds resistance to compression for the expanded stent, among other things. It is longitudinally flexible in both the unexpanded and expanded conditions. It has several embodiments.
An important part of the new configuration includes a spiral or spiral-like structure comprised of joined elements which are coiled or bent and which unwind, uncoil or unbend to a more or less straightened condition on expansion of the stent. Such structures are hereinafter referred to collectively as spirals, spirals or spiral-like structures. These structures provide regions of low strain in the stent during expansion. These elements may be joined to each other or to any radially expansive members of any kind, annular serpentine members being preferred.